1. Field of the Invention
The present invention relates to a copolycarbonate diol. More particularly, the present invention is concerned with a copolycarbonate diol comprising:    (a) recurring units each represented by the following formula (1):     (b) recurring units each independently represented by the following formula (2):             wherein n is 4, 5 or 6; and            (c) terminal hydroxyl groups,
wherein the copolycarbonate diol has a number average molecular weight of from 300 to 20,000, and wherein the amount of the recurring units (a) is from 10 to 90% by mole, based on the total molar amount of the recurring units (a) and (b).
The copolycarbonate diol of the present invention is a liquid having low viscosity. Therefore, the copolycarbonate diol of the present invention is easy to handle, as compared to the conventional polycarbonate diols which are solids or highly viscous liquids. Hence, the copolycarbonate diol of the present invention is advantageous for various uses, such as a raw material for producing a thermoplastic elastomer (such as a thermoplastic polyurethane) used for producing various shaped articles (for example, a spandex, which is a polyurethane elastomeric fiber); a component for a coating material or an adhesive; and a polymeric plasticizer.
The present invention is also concerned with a thermoplastic polyurethane obtained from the above-mentioned copolycarbonate diol and a polyisocyanate. The thermoplastic polyurethane of the present invention exhibits excellent properties with respect to flexibility, heat resistance, low temperature properties, weathering resistance, strength, and molding processability. Therefore, the thermoplastic polyurethane of the present invention is extremely useful as a material for producing various shaped articles, such as automobile parts, parts for household electric appliances, toys and sundry goods. Especially, the thermoplastic polyurethane of the present invention is useful for producing shaped articles which are required to have high strength, such as hoses, sheets and industrial belts; and shaped articles which are required to have high flexibility, such as interior and exterior parts for automobiles (for example, window moles, bumpers, skin parts for an instrument panel, and grips), spandexes, bands for wristwatches, and shoe soles.
2. Prior Art
A polyurethane and a urethane-, ester- or amide-based thermoplastic elastomer are used in the art. The soft segments of the polyurethane and thermoplastic elastomer are composed of structural units formed from a polyester polyol and/or a polyether polyol, each of which has a hydroxyl group at each of the molecular terminals thereof (see, for example, U.S. Pat. Nos. 4,362,825 and 4,129,715). A polyester polyol, such as a polyadipate polyol, has poor hydrolysis resistance. Due to the poor hydrolysis resistance, for example, a polyurethane containing, as soft segments, structural units formed from a polyester polyol has a disadvantage in that tackiness and cracks are likely to occur on the surfaces of shaped articles of the polyurethane within a relatively short period of time. Therefore, the use of such a polyurethane is considerably limited. On the other hand, a polyurethane containing, as soft segments, structural units formed from a polyether polyol has good hydrolysis resistance and excellent flexibility. However, the polyurethane has a disadvantage in that it has poor resistance to light and oxidative degradation. The disadvantages of these polyurethanes are, respectively, attributed to the presence of ester groups in the polymer chain and the presence of ether groups in the polymer chain.
With respect to the polyester- or polyamide-based thermoplastic elastomer containing, as soft segments, structural units formed from a polyester polyol or a polyether polyol, there has recently been a demand for improvement in resistance to heat, light, hydrolysis and oil. In accordance with the increased demand for such improvement, the same disadvantages as accompanying the above-mentioned polyurethanes have been pointed out with respect also to the thermoplastic elastomer.
A polycarbonate polyol prepared from 1,6-hexanediol is used as a polyol usable for forming soft segments which have excellent resistance to hydrolysis, light, oxidative degradation, heat and the like. These resistances are due to the fact that carbonate linkages in the polymer chain exhibit extremely high chemical stability.
However, the polycarbonate polyol prepared from 1,6-hexanediol is crystalline and hence is a solid at room temperature. Therefore, for producing a polyurethane from the polycarbonate polyol and a polyisocyanate, it is necessary that the polycarbonate polyol be heated and melted before effecting a reaction with the polyisocyanate, so that a long period of time is required for producing a polyurethane. In this respect, the polycarbonate polyol poses a problem in handling.
As mentioned above, when this polycarbonate polyol is used for forming soft segments of a polyurethane, the polyurethane has improved resistance to hydrolysis, light, oxidative degradation and heat. However, the polyurethane has defects in flexibility and low temperature properties. Especially, the polyurethane is defective in that it exhibits markedly poor elastic recovery at low temperatures. Due to such defects, the polyurethane poses a problem in that it exhibits poor stringiness and hence has poor spinnability. The reason for the poor stringiness is that crystallization is likely to occur in the soft segments of the polyurethane, thus leading to a lowering of the elasticity of the polyurethane. Such easy occurrence of crystallization in the soft segments results from the high crystallinity of the polycarbonate polyol prepared from 1,6-hexanediol.
In order to solve these problems, it has been proposed to copolymerize 1,6-hexanediol with a polyhydric alcohol having a side chain so as to produce a copolycarbonate polyol.
For example, in Unexamined Japanese Patent Application Laid-Open Specification No. Hei 10-292037, a polycarbonate containing recurring units derived from 1,6-hexanediol and neopentyl glycol, is disclosed. This polycarbonate is used as a material for a polyurethane, a polyamide elastomer and a polyester elastomer, and as a component for a coating material and an adhesive.
In Japanese Patent No. 2781104 (corresponding to EP 562 577), a polycarbonate polyol containing recurring units derived from a diol having a branched structure and a polyhydric alcohol comprising a tetrahydric to hexahydric alcohol, is disclosed. This polycarbonate polyol is used as a binder for a coating material.
In Unexamined Japanese Patent Application Laid-Open Specification No. Hei 2-49025 (corresponding to EP 343 572), a polycarbonate diol containing recurring units derived from a C3-C20 polyhydric alcohol having a side chain and 1,6-hexanediol, is disclosed. This polycarbonate diol is used as a material for producing a polyurethane.
In Japanese Patent No. 2506713, a polycarbonate diol containing recurring units derived from 2-methyl-1,8-octanediol or recurring units derived from a diol comprised mainly of 2-methyl-1,8-octanediol and 1,9-nonanediol, is disclosed. This polycarbonate diol is used as a material for producing a polyurethane, a polyamide elastomer and a polyester elastomer, and is used in the fields of a coating material and an adhesive.
WO 98/27133 discloses a polycarbonate polyol containing recurring units derived from a diol having a side chain which contains two lower alkyl groups, and a polyurethane produced using, as a soft segment, this polycarbonate polyol.
These polycarbonate polyols have a side chain, and, therefore, the elastomers (such as polyurethanes) produced using, as a soft segment, these polycarbonate polyols, have a side chain, i.e., they have a branched structure. Due to such branched structure, the polycarbonate polyols have a problem in that the elastomers produced using these polycarbonate polyols exhibit poor mechanical properties, as compared to those of elastomers which have no side chains.
When a thermoplastic elastomer is produced using, as a soft segment, a polycarbonate polyol prepared from a bulky polyhydric alcohol (e.g., neopentyl glycol) which contains a quaternary carbon atom having two side chains bonded thereto, the strength of the thermoplastic elastomer is lowered depending on the content of the recurring units derived from the above-mentioned bulky polyhydric alcohol.
When a thermoplastic elastomer is produced using, as a soft segment, a polycarbonate polyol prepared from a polyhydric alcohol which contains a tertiary carbon atom having one side chain bonded thereto, there is a problem in that the heat aging resistance of the thermoplastic elastomer is lowered. The reason for occurrence of such a low heat aging resistance of the thermoplastic elastomer is that the hydrogen atom which is bonded to the tertiary carbon atom having one side chain is likely to become a radical so as to be easily eliminated from the tertiary carbon atom, as compared to a hydrogen atom which is bonded to a secondary carbon atom having no side chains.
As another measure for lowering the crystallinity of a polycarbonate polyol prepared from 1,6-hexanediol, it has been proposed that 1,6-hexanediol is copolymerized with a diol having no side chains so as to produce a copolycarbonate diol.
For example, Examined Japanese Patent Application Publication No. Hei 5-29648 (corresponding to EP 302 712 and U.S. Pat. Nos. 4,855,377 and 5,070,173) discloses an aliphatic copolycarbonate diol produced using 1,5-pentanediol and 1,6-hexanediol.
Generally, even when a homopolymer which is obtained by homopolymerizing a monomer is crystalline, a copolymer which is obtained by copolymerizing the monomer with an appropriate comonomer has low crystallinity, as compared with the homopolymer; the reason for this is that the structural regularity of the copolymer is disordered by the comonomer units. In the case of a copolycarbonate polyol containing 1,6-hexanediol units, when the comonomer diol units are, for example, those derived from a diol which contains an odd number of methylene groups, such as 1,5-pentanediol, the structural regularity of the copolycarbonate polyol is likely to be greatly disordered, as compared to the case where the comonomer diol units are those derived from a diol which contains an even number of methylene groups.
However, this copolycarbonate diol is a solid or a viscous liquid, so that the handling properties of the copolycarbonate diol are unsatisfactory, depending on the use thereof.
In recent years, a thermoplastic polyurethane which is produced using, as a soft segment, a copolycarbonate diol prepared from a mixture of 1,6-hexanediol and 1,4-butanediol or 1,5-pentanediol is attracting attention because of its great advantages. (The above-mentioned copolycarbonate diol is disclosed in Examined Japanese Patent Application Publication No. Hei 5-029648 (which is mentioned above) and Japanese Patent No. 3128275; and the above-mentioned thermoplastic polyurethane is disclosed in Unexamined Japanese Patent Application Laid-Open Specification No. Hei 5-51428 and Japanese Patent No. 1985394 (corresponding to EP 302 712 and U.S. Pat. Nos. 4,855,377 and 5,070,173).) Specifically, such thermoplastic polyurethane has advantages in that it has remarkably excellent properties with respect to flexibility and low temperature properties, as well as the same excellent properties as mentioned above and as achieved by using, as a soft segment, a polycarbonate diol prepared from 1,6-hexanediol, i.e., excellent resistance to hydrolysis, light, oxidative degradation and heat.
However, in the course of the studies of the present inventors, it was found that the thermoplastic polyurethane produced using, as a soft segment, the above-mentioned copolycarbonate diol has a problem in that the flexibility is still unsatisfactory and hence the use of the thermoplastic polyurethane is limited.
With respect to polycarbonate diols other than those mentioned above, there are documents which refer to the use of a polycarbonate diol prepared from 1,3-propanediol.
For example, in WO 01/72867, there is disclosed a thermoplastic polyurethane produced using, as a soft segment, a polycarbonate diol in which the diol units are composed only of 1,3-propanediol units. However, this thermoplastic polyurethane is hard and exhibits high modulus (that is, the elongation of the thermoplastic polyurethane is unsatisfactory), rendering it difficult to use the thermoplastic polyurethane in the same application fields as those of the ordinary elastomers. The reason for this has not yet been completely elucidated; however, the reason is presumed to be as follows.
In the above-mentioned polycarbonate diol, each recurring unit has only three methylene groups (derived from 1,3-propanediol), so that the ratio of the carbonate linkages in the polycarbonate diol molecule is high. The flexibility of such polycarbonate diol molecule is lowered, and hence, the thermoplastic polyurethane produced using such polycarbonate diol exhibits low elasticity.
Examined Japanese Patent Application Publication No. Hei 8-32777 discloses a process for rapidly producing a polycarbonate diol, comprising subjecting a mixture of a dialkyl carbonate and a hydroxy compound or a mixture of a diaryl carbonate and a hydroxy compound to a transesterification reaction in the presence of a titanium compound or a tin compound. This process is intended to rapidly produce a high quality polycarbonate diol which is less likely to suffer discoloration.
In this prior art document, as examples of hydroxy compounds, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol are described. However, in this prior art document, no polycarbonate diol is actually produced using 1,3-propanediol. Further, no polyurethane is produced using a polycarbonate diol, and no evaluation is made with respect to the properties of a polyurethane.
Unexamined Japanese Patent Application Laid-Open Specification No. Hei 4-239024 discloses the following process. First, a reaction mixture which contains a low molecular weight polycarbonate diol is produced. A diaryl carbonate is added to the reaction mixture produced, and a reaction is performed while removing a by-produced alcohol, thereby producing a high molecular weight polycarbonate diol. This process is intended to produce a polycarbonate diol using a monomer in a small amount.
In this prior art document, as examples of diols which are usable as a material for producing the polycarbonate diol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol are described. However, in this prior art document, no polycarbonate diol is produced using 1,3-propanediol. Further, no polyurethane is produced using a polycarbonate diol, and naturally, any evaluation is not made with respect to the properties of a polyurethane.
As apparent from the foregoing, conventionally, there has not yet been obtained a polycarbonate diol which is suitable as a material for producing a thermoplastic polyurethane which is advantageous not only in that it exhibits excellent resistance to hydrolysis, light, oxidative degradation and heat, but also in that it exhibits excellent properties with respect to flexibility and low temperature properties.